Cosmic ice could breed life

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Could cosmic ice clouds seed life on Earth? Life on Earth depends on a range of complex chemicals, including sugars that are used in genetic material like DNA and its relative, RNA. But it's always been a mystery how these molecules got here in the first place.

Now a new study by scientists in France suggests that, if they are zapped by ultraviolet rays from nearby newly-formed stars, chemicals contained in clouds of ice particles drifting in space can be converted into much more complex substances, like sugars.

Writing in PNAS, CNRS scientist Pierre de Marcellus and his colleagues made mixtures of water, methanol and ammonia which they cooled to -200 Celsius and placed under low pressure to simulate the environment of interstellar space.

The resulting "ices" were simultaneously irradiated for several days with UV waves similar in energy to the light produced by a newborn star. When the ices later thawed, just as they would have done had they landed on a young, warm planet, a brownish residue known colloquially to scientists in the field as "yellow gunk" was left behind.

When this was analysed, the French team uncovered the molecular signatures of a family of chemicals known as aldehydes, including two sugars called glycolaldehyde and glyceraldehyde. These have been shown recently to be precursors for the formation of RNA molecules, which are widely regarded as the first form of genetic material to exist on Earth.

The results, say the scientists, show that a likely source of some of the essential ingredients needed to bake "life's cake" were these irradiated ice clouds in interstellar space. Comets, asteroids and other impacts would have delivered these substances to a young planet, potentially equipping it with the necessary chemicals to kickstart life.

The researchers also point out that their data could prove valuable to the Rosetta team currently engaged in studying the comet 67P-Churyomov-Gerasimenko. The Philae lander, which succesfully landed on the comet last year, "carries a device specifically designed for the characterisation of organic molecules," like those detected by the CNRS team...